An oxygen pump sensor requires a vent in order to operate where oxygen gas is consumed at the sensing electrode and generated at the counter electrode. A connection to the exterior atmosphere is therefore required when the counter electrode is placed at the base of the electrode stack in order to vent the generated oxygen from inside the sensor. One method of providing venting to the counter electrode at the base of the stack is to extend a molded tube to meet the electrode (e.g., the City Technology, ECO-OX).
An electrode stack within an oxygen pump sensor also requires adequate physical support to maintain consistent stack compression. The compression of the electrode stack facilitates electrical contact with the current collectors, and ensures adequate transfer of electrolyte to the separators within the stack.